Sub-domains vs Sub-directories
...because the difference is significant – by Ginette Degner

Here's a tricky question...

What's the difference between a sub-domain and a sub-directory?

If you know the answer, congratulations! ...if you're scratching your puzzled head, don't stress, you have plenty of company among the confused.

Answer:

A sub-directory looks like this:  http://www.yourdomain.com/alligators
While a sub-domain looks like this:  http://alligators.yourdomain.com

No doubt you've seen plenty of examples. Some notable ones include;

sports.yahoo.com travel.yahoo.com news.bbc.co.uk

money.cnn.com sportsillustrated.cnn.com travel.americanexpres.com

news.google.com froogle.google.com travel.state.gov

...each being a separate entity or section within a main site. So now you're probably wondering 'what's the reasoning? ...why not just use the more common sub-directory?'  I'm glad you asked.

Special treatment for a special class...

Used smartly, sub-domains can gain a URL special treatment compared to sub-directories. For instance;

• They can be used to create top-level domain names within your primary domain name. By replacing the 'www' in your domain name with a specific keyword that describes a category or product, you gain the advantage of having a keyword-rich domain name without having to register (and maintain) a separate unique domain.

• They provide an efficient way to place your keyword into your domain name without having to procure the perfect dot.com or settle for a subdirectory which would mean a longer, a...